The present invention relates to counterbalancing mechanisms, and, more specifically, those used in opto-mechanical assemblies of infrared imaging systems.
Such systems often include a pivoting planar mirror assembly whose rotation is motor driven to provide a means of optically scanning a scene of interest. This type of mirror may be quite heavy, and, therefore, require counterbalancing to provide necessary rotational response while minimizing power requirements of the driving motor, or to prevent degradation in system performance, especially under shock and vibration conditions.
In the past, counterbalancing of this type of scanning mirror has been achieved by placing the center of gravity of a counterweight of appropriate mass on a plane described by the center of gravity of the mirror and the line which the mirror rotates about, such that the center of gravity of the mirror, counterweight and pivot point are colinear, and such that the center of gravity of the mirror and counterweight are on either side of the pivot axis. The mass and location of the counterweight can be determined by the following relationship: EQU m.sub.1 d.sub.1 =m.sub.2 d.sub.2 ;
where m.sub.1 and m.sub.2 are the respective masses of the mirror and counterweight, and d.sub.1 and d.sub.2 are the respective moment arm distances between the centers of gravity of m.sub.1 and m.sub.2 and the pivot point, as measured perpendicular to the pivot axis. In addition to providing balancing in all directions, this arrangement provides increased resistance to shock and vibration damage which are often required in these systems. The disadvantage of this approach is that the counterweight is often in a position which requires a significant increase in volume of the total scan system, or the counterweight requires positioning that will not fit within the system's physical boundaries.
It is, accordingly, a primary object of the present invention to provide a means for counterbalancing an opto-mechanical scanning mechanism where spacial constraints of the packaging of the system would normally preclude adequate counterweighting.